Would you use a mod which simply awarded you every achievement without you doing anything? If not, why not? It's not really any different to being awarded the achievements in a game altered by mods - either way, you're not doing what the achievement was intended to be awarded for.
Nope.
I've not installed any mods that I would consider as knocking the game balance out of kilter. I tend to install bug-fixing or cosmetic mods more than anything because as soon as I feel like I'm using a cheat, I become bored quickly and stop playing.
But yeah, I'm not the sort that has to have 100% achievements on each game but the odd few are quite good fun to go for, so I was irked by the system being disabled.